ADDITIONAL SYSTEM INFORMATION :
Its crashes on Win7 64bit, and Linux 64bit (manjaro).
Tested on Jdk 10.0.2 and 11.0.1

A DESCRIPTION OF THE PROBLEM :
JVM crashes wen we load 2 times following HTML to JavaFX WebView component:


<blockquote class=\"twitter-tweet\"><a href=\"https://twitter.com/stu_bot3000/status/793389598227529728?ref_src=twsrc%5Etfw\"></a></blockquote>\n" +
                    "<script src=\"https://platform.twitter.com/widgets.js\"></script>


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Load given HTML to WebView, wait for a while to load content completely, and set this html content again.


---------- BEGIN SOURCE ----------
import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Scene;
import javafx.scene.web.WebView;
import javafx.stage.Stage;

public class Main extends Application {

    public static void main(String[] args) {
        Application.launch(args);
    }

    @Override
    public void start(Stage primaryStage) {
        try {
            WebView webView = new WebView();

            Scene scene = new Scene(webView, 800, 600);
            primaryStage.setScene(scene);
            primaryStage.show();

            String crashHtml = "<blockquote class=\"twitter-tweet\"><a href=\"https://twitter.com/stu_bot3000/status/793389598227529728?ref_src=twsrc%5Etfw\"></a></blockquote>\n" +
                    "<script src=\"https://platform.twitter.com/widgets.js\"></script>";

            webView.getEngine().loadContent(crashHtml);

            new Thread(() -> {
                try {
                    System.out.println("Wait 5 sec to full load, then set this content again...");
                    Thread.sleep(5000);
                    Platform.runLater(() -> {
                        System.out.println("Reloading... and crash...");
                        webView.getEngine().loadContent(crashHtml);
                    });
                } catch (Exception e) {
                }
            }).start();


        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
---------- END SOURCE ----------

FREQUENCY : always